Liverpool manager Jurgen Klopp and Tottenham boss Ange Postecoglou led a chorus of disapproval on Friday over a controversial proposal to introduce blue cards and sin bins.
It has been reported that blue cards will be shown to players, who would be sent to a 'sin-bin' for 10 minutes, as part of a new trial aimed at improving on-pitch behaviour.
At present, players shown a red card or two yellow cards are expelled for the rest of the game.
Sin bins have been used at grassroots level in England for dissent, but the trial could also include cynical fouls.
Reports say that football's lawmakers IFAB have delayed releasing information about the proposed trial following talks with world governing body FIFA.
It is understood that the trial phase will not take place in top-level football to avoid players being in competitions with different rules concurrently.
But Klopp was among several Premier League managers to express concerns about the proposal.
"I think everything what the actual situation shows is we should keep it as simple as somehow possible, for the referees as well," the German said Friday.
"It's a difficult job. I think the introduction of a blue card would just give more opportunities to fail as well.
"The discussion will be: 'It was a blue card, should it have been a yellow card? Now it's 10 minutes off. In the good old times it would have been a red card or only a yellow'.
"It doesn't sound like a fantastic idea in the first moment but actually I can't remember the last fantastic idea (which) came from these guys, if they ever had one. I am 56 and, pah, never."
Postecoglou said the plan could be another misstep by football's authorities after the controversial introduction of the widely criticised VAR system.
"I don't think people will be surprised by my thoughts on it. I struggle to understand this urgency all of a sudden to bring in new things," he said.
"I don't know if there's that much wrong with the game as I see it. My biggest issue with the game right now is that VAR has changed the experience, whether you're a player, a manager or a supporter.
"Beyond that, I don't know why a different colour card is going to make any difference."
Arsenal boss Mikel Arteta called for the proposals to be rigorously tested before blue cards are given the green light.
"We've got a lot going on with decisions, with technology. I don't know if we are ready for that yet," he said.
"Who knows (if it is a good idea). Hopefully it's going to be tested very well before they introduce it at this level."
AFP